Study of long-term flux and photon Index distributions of blazars using RXTE observations

TL;DR

This study analyzes 16 years of RXTE data to understand flux and photon index distributions of blazars, revealing different statistical behaviors for FSRQ and BL Lac types and supporting the two flux states hypothesis.

Contribution

It provides the first detailed long-term statistical analysis of flux and index distributions for multiple blazars, highlighting differences between FSRQ and BL Lacs and proposing a double log-normal flux distribution model.

Findings

FSRQ 3C273 has a log-normal flux and Gaussian index distribution.

BL Lacs Mkn501 and Mkn421 show non-Gaussian, likely double log-normal flux distributions.

Flux distribution differences suggest distinct behaviors of low and high energy electrons.

Abstract

We present a detailed study of flux and index distributions of three blazars (one FSRQ and two BL Lacs) by using 16 years of Rossi X-ray Timing Explorer archival data. The three blazars were chosen such that their flux and index distributions have sufficient number of data points ($\geq$90) with relatively less uncertainty ($\bar{\sigma_{err}^{2}}/\sigma^{2}$<0.2) in light curves. Anderson-Darling (AD) test and histogram fitting shows that flux distribution of FSRQ 3C273 is log-normal, while its photon index distribution is Gaussian. This result is consistent with linear Gaussian perturbation in the particle acceleration time-scale, which produces log-normal distribution in flux. However, for two BL Lacs viz. Mkn501 and Mkn421, AD test shows that their flux distributions are neither Gaussian nor log-normal, and their index distributions are non-normal. The histogram fitting of Mkn501 and Mkn421, suggests that their flux distributions are more likely to be a bi-modal, and their index distributions are double Gaussian. Since, Sinha et al. (2018) had shown that Gaussian distribution of index produces a log-normal distribution in flux, double Gaussian distribution of index in Mkn501 and Mkn421 indicates that their flux distributions are probably double log-normal. Observation of double log-normal flux distribution with double Gaussian distribution in index reaffirms two flux states hypothesis. Further, the difference observed in the flux distribution of FSRQ (3C273) and BL Lacs (Mkn501 and Mkn421) at X-rays, suggest that the low energy emitting electrons have a single log-normal flux distribution while the high energy ones have a double log-normal flux distribution.